discovery of barium. The same holds for the discoveries of all of the lanthanides
and many other metals, which are usually attributed to the chemist who first isolated
the oxide.
It was Gahn who found that the earth isolated by Scheele was identical to the
earth obtained from baryte (known in Swedish as tungspat, heavy spar). The discovery was made in spring 1774, and Scheele got the news in a now lost letter.
Scheele replied on May 16, acknowledging the discovery. This was a major
breakthrough, as baryte was a more convenient source for the new earth than the
erratic appearance in pyrolusite. Gahn, as usual, never published anything, but the
discovery was announced by Bergman: “The new earth, which Scheele mentions in
his paper on [pyrolusite], is actually the basis in heavy spar, which Mr. J. G. Gahn
discovered recently” [14]. Bergman introduced the name earth of heavy spar
(Chap. 26), and was the first to use barium chloride as a reagent to detect sulphate
(Sect. 23.3). In a paper on the analysis of sea water he wrote:
Solution of heavy earth [BaO] in acid of salt [hydrochloric acid] soon precipitated a white
powder [BaSO 4 ], which did not dissolve in boiling water, but had the appearance of heavy
spar [BaSO 4 ], and showed that vitriolic [sulphuric] acid was present [in sea water]. This test
is the most reliable of all known tests to reveal vitriolic acid, even when the amount is so
small that it is unnoticed in any other manner. [15]
The discovery of a new elemental earth was remarkable, given that only a
handful of earths had been recognised. Silica (SiO 2 ) and lime (CaO) had been
known since centuries, but it was not until 1754 that Marggraf showed that alum
contained a special earth (Al 2 O 3 ) and the following year Joseph Black (1728–1799)
distinguished magnesia (MgO) from lime [16]. Scheele realised the possibility that
earth of heavy spar could be reduced to a metal, and several years later he wrote to
Wilcke:
Extraordinary, that my experiments with tungsten, molybdena and Magnesia nigra [MnO 2 ]
have given reason to these new metals’ discovery: let’s see if not the earth in heavy spar
[BaO] with some tweaking also will be added to the metals after reduction.
The low reduction potential and reactive nature of barium made such a reduction
impossible in the eighteenth century. Early in the following century Berzelius and
Pontin electrolysed moist barium hydroxide with a mercury cathode, which afforded barium amalgam. Metallic barium was, as already mentioned, first isolated by
Davy in 1808 [17].
15.3 The Isolation of Metallic Manganese
It is possible that manganese had been prepared before Scheele’s studies. It is, for
example, possible that Kaim prepared manganese in 1770, [18] but his results are
unverified and gained little recognition. Throughout his magnesia paper, Scheele
referred to MnO 2 as an earth, but in a comment, following directly after Scheele’s
paper, Bergman suggested that it might instead be a metal oxide (metal calx): “on
15.2 The Discoveries of Chlorine and Barium
217
and many other metals, which are usually attributed to the chemist who first isolated
the oxide.
It was Gahn who found that the earth isolated by Scheele was identical to the
earth obtained from baryte (known in Swedish as tungspat, heavy spar). The discovery was made in spring 1774, and Scheele got the news in a now lost letter.
Scheele replied on May 16, acknowledging the discovery. This was a major
breakthrough, as baryte was a more convenient source for the new earth than the
erratic appearance in pyrolusite. Gahn, as usual, never published anything, but the
discovery was announced by Bergman: “The new earth, which Scheele mentions in
his paper on [pyrolusite], is actually the basis in heavy spar, which Mr. J. G. Gahn
discovered recently” [14]. Bergman introduced the name earth of heavy spar
(Chap. 26), and was the first to use barium chloride as a reagent to detect sulphate
(Sect. 23.3). In a paper on the analysis of sea water he wrote:
Solution of heavy earth [BaO] in acid of salt [hydrochloric acid] soon precipitated a white
powder [BaSO 4 ], which did not dissolve in boiling water, but had the appearance of heavy
spar [BaSO 4 ], and showed that vitriolic [sulphuric] acid was present [in sea water]. This test
is the most reliable of all known tests to reveal vitriolic acid, even when the amount is so
small that it is unnoticed in any other manner. [15]
The discovery of a new elemental earth was remarkable, given that only a
handful of earths had been recognised. Silica (SiO 2 ) and lime (CaO) had been
known since centuries, but it was not until 1754 that Marggraf showed that alum
contained a special earth (Al 2 O 3 ) and the following year Joseph Black (1728–1799)
distinguished magnesia (MgO) from lime [16]. Scheele realised the possibility that
earth of heavy spar could be reduced to a metal, and several years later he wrote to
Wilcke:
Extraordinary, that my experiments with tungsten, molybdena and Magnesia nigra [MnO 2 ]
have given reason to these new metals’ discovery: let’s see if not the earth in heavy spar
[BaO] with some tweaking also will be added to the metals after reduction.
The low reduction potential and reactive nature of barium made such a reduction
impossible in the eighteenth century. Early in the following century Berzelius and
Pontin electrolysed moist barium hydroxide with a mercury cathode, which afforded barium amalgam. Metallic barium was, as already mentioned, first isolated by
Davy in 1808 [17].
15.3 The Isolation of Metallic Manganese
It is possible that manganese had been prepared before Scheele’s studies. It is, for
example, possible that Kaim prepared manganese in 1770, [18] but his results are
unverified and gained little recognition. Throughout his magnesia paper, Scheele
referred to MnO 2 as an earth, but in a comment, following directly after Scheele’s
paper, Bergman suggested that it might instead be a metal oxide (metal calx): “on
15.2 The Discoveries of Chlorine and Barium
217